Download Types of Joints Components of Joints Joint mechanics

Joint Structure and Function
Types of Joints
Components of Joints
Joint mechanics
Dave Buttle K131 <[email protected]>
The Function of Joints
• To allow movement in 3-dimensions
• To bear weight
• To transfer the load evenly to the
musculoskeletal system
Tissues associated with joints
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Bone
Muscle
Cartilage
Synovium
Synovial fluid
Dense fibrous tissue/
capsule, tendons and
ligaments
Types of joints – structural classification
Fibrous
e.g. teeth sockets
http://rst.gsfc.nasa.gov/Intro/Part2_26b.html
Cartilaginous
Synovial
e.g. intervertebral discs
e.g. metacarpophalangeal
Types of joints – functional
classification
1. Synarthroses - immovable joints, mostly fibrous
(eg. skull sutures)
2. Amphiarthroses - slightly moveable joints,
most cartilaginous (eg. intervertebral discs)
3. Diarthroses - freely moveable joints, mostly
synovial (eg. hip)
Fibrous joints 1- Sutures
Occur only between bones of the skull (allow skull
growth in development)
Adjacent bones interdigitate
Junction filled with very short tissue fibres
To allow growth after birth a baby has
fibrous tissue between skull bones which
develops into sutures
Foetal
Fibrous joints 2 - Syndesmoses
Bones are connected by a cord (ligament) or sheet
(interosseous membrane) of fibrous tissue.
Amount of movement permitted is proportional to
length of fibre
Fibrous joints 3 - Gomphoses
A peg-in-socket fibrous joint found only in tooth
articulation
Cartilaginous joints - Synchondroses
The bones are directly connected by hyaline
cartilage. These are usually amphiarthroses ie.
slightly moveable eg. costal cartilage of the ribs
Cartilaginous joints - Symphyses
Here the connecting cartilage is a pad or plate
of fibrocartilage eg. Intervertebral discs
Intervertebral disc
Designed to take
load; water-binding
proteoglycan-rich
nucleus pulposus
surrounded by
tough fibrous
annulus fibrosus – a
shock absorber
Joint Classification Summary
Fibrous Synarthrosis
Suture
Syndesmosis
Gomphosis
Synchondrosis
Cartilaginous Amphiarthrosis
Symphysis
Synovial Diarthrosis
Synovial Joints
Articulating bones are separated by a fluid-filled
cavity
Most joints of the body fit into this category
There are five characteristic features of synovial
joints….
Synovial Joints - components
1. Articular cartilage
2. Joint capsule -the
inner layer is the synovial
membrane,
3. Joint (synovial) cavity
- a space filled with
synovial fluid.
4. Synovial fluid
5. Reinforcing ligaments
Types of Cartilage
Additional components associated
with some synovial joints
1. Bursae – fluid filled sacs lined by synovial
membrane
2. Menisci – Discs of fibrocartilage
Articular (Hyaline) Cartilage
Almost frictionless surface
Resists compressive loads
High water content
Low cell content
No blood supply
Hyaline Cartilage: The secret to a pain-free joint.
Low friction coefficient = friction-free articulation!
Cartilage: Composition
Water, proteoglycans, collagen
Hyaline cartilage
Fibrocartilage
Hyaline cartilage
Fibrocartilage
Annulus fibrosus
Nucleus pulposus
Articular Cartilage: Structure
Alignment of collagen fibrils
Articular cartilage zones
Superficial
Middle
Deep
Kim et al. Osteoarthritis and Cartilage (2003) 11, 653–664
Synovial Fluid – the joint lubricant
• Covers articulating surfaces with
thin film (e.g. healthy knee just 0.5
ml fluid)
• Modified from plasma by synovial
membrane (synoviocytes)
• Fluid, proteins, charged sugars
that bind water eg. hyaluronate
• Result: slimy fluid (like egg white)
• Reduces friction during
articulation
Synovial membrane
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Sits on the joint capsule
and encloses synovial
cavity
•
Only a few cells thick
•
Can have villi and
projections to increase
surface area
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Secretes synovial fluid
components eg.
hyaluronate
synoviocytes
Blood
vessel
connective
tissue
http://www.anatomy.dal.ca/Human_Histology/Lab6/2LH12.html
Tendons and Ligaments
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Ligaments: connect bone to bone
Stabilise joints
Similar to a tendon but with less regularly arranged
fibres
Can stretch up to 6% before breaking and may
contain more elastic fibres than tendon
(generalisation)
ligament
muscle
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Tendons: connect bone to muscle
Stabilise joints
Made of dense regular connective tissue, rich in
type I collagen
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Allow muscles to be accommodated at a distance
from their insertion, e.g. muscles of the forearm
move the fingers. Provides a solid base (insertion to
bone) on which muscles can pull
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Muscles also stabilise joints
Tendon structure – the use of
collagen modules (tropocollagen)
and hierarchical structure
The musculotendinous
junction – where most
ruptures occur
Joint Mechanics: A synovial joint is the
fulcrum of a lever system
A lever can apply a torque (twist) about a fulcrum,
proportional to force x distance
In a first class lever, the fulcrum is in
the middle (the elbow joint) the force
is at one end (the triceps muscle)
and the resistance is at the other end
(the weight being pulled).
In a second class lever, the fulcrum is
at one end (eg. Temperomandibular
joint) the force is at the other end (the
muscles of the chin) and the
resistance is in the centre (the
muscles attached to the coronoid
process).
In a third class lever, the fulcrum is at
one end (eg. elbow joint), the force is
in the middle (the biceps muscle) and
the resistance is at the other end (the
weight being pulled).
Movement of synovial joints
Body movements
Examples of synovial joints – Hip Joint
Ball and socket joint
Held securely in place by strong ligaments and heavy
cylindrical joint capsule
Hip joint ligaments
Main stabilising ligaments:
Iliofemoral
Pubofemoral
Ischiofemoral
The shoulder
A ball and socket joint
Stability sacrificed for range of movement. Joint capsule is loose.
Dislocation of the shoulder quite common. The rotator cuff muscles
help in stabilisation but are prone to injury, especially at tendon
insertion sites
Ligaments stabilising the shoulder
Glenoidal labrum - fibrocartilage
Coracohumeral ligament
Three glenohumeral ligaments
Transverse humeral ligament
Tendons and Muscles stabilising the
shoulder
Long head of Biceps brachii
Tendons of the rotator cuff: subscapularis, supraspinatus,
infraspinatus and teres minor
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Knee Joint – complex!
Not a hinge joint, femur/tibia is
condyloid (ovoid head of one bone
moves in an elliptical cavity of
another) and femur and patella
gliding. Joint capsule thin but
strengthened by many tendons
and ligaments
Knee joint – ligaments
Injuries to weight-bearing joints
• Can cause changes in the stability of the
joint which can lead to inappropriate
weight-bearing and the development of
osteoarthritis later in life
• Beware, all you sports-people
Elbow Joint
Classic hinge joint between
humerus and ulna and
gliding joint between
humerus and radius
Single joint cavity but synovial
membrane partly divides ulnar
and radial portions
Humerus
Joint capsule
Synovial membrane
Joint cavity
Articular cartilage
Coranoid process
Troclea
Olecranon process
Radius
Ulna
Ligaments and tendons at the elbow
Medial
Lateral
Conclusions
Joints are spaces between bones bridged by fibrous and/or cartilaginous
tissue
Cartilaginous joints allow more movement than fibrous joints, synovial joints
allow the most movement
In synovial joints the bone ends are covered by cartilage to aid friction-free
movement and absorb compressive stresses
Synovial fluid in the joint cavity increases lubrication of the joint
Ligaments and tendons, dense connective tissue, stabilise the joints